radiobutton-type fields NOT being evaluated right

required steps:
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create a content type X with fields of type "list" (regardless text, float,integer) with widget "Check boxes/radio buttons"
set fields to required
don't set default values
set allowed values[and labels] other than 0

add content->type X -> submit without selecting any radio-fields

expected behaviour:
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message "required field..."

unexpected result:
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message "illegal choice..."

if you change the fields above so they have an allowed value 0, things get a new twist:
unexpected result:
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a) submitting the node will validate, but viewing the node,
you will (as expected, since you cose nothing) see no content for your field.

b) if the label is 0 too, 0 as label is not being rendered in html

i saw a number of similar forum-posts and issues, but none seemed to mention all this.
sorry if i create a duplicate...